BACKGROUND: This work was carried out to investigate and analyze the interrelated dynamics of mass transport, membrane fouling and flux decline during nanofiltration of tartrazine. A combined application including pore diffusion transport model and a material balance approach was used to model an experimental flux data obtained from different values of pH (3, 5, 7 and 10), feed-dye concentration (25, 100 and 400 mg L-1), and transmembrane pressure (1200, 1800 and 2400 kPa). RESULTS: Almost 100% dye solution removal and a permeate flux of 135 L m(-2) h(-1) were obtained for 25 mg L-1 and 1200 kPa at pH 10. At pH 10, lower membrane fouling was obtained due to the increase of electrostatic repulsion between anionic dye molecules and the more negatively charged membrane surface. Flux decline and membrane fouling increased together with transmembrane pressure and dye concentration. Fouling was found to be directly related to proportional-permeation coefficient (k(O)') of dye which was identified as the solute passing into the permeate with respect to the amount transported into the membrane from the feed. CONCLUSIONS: For a decrease of pH (10 to 3) and transmembrane pressure (2400 to 1200 kPa) or an increase of feed-dye concentration (25 to 400 mg L-1), fewer dye molecules passed into the permeate with respect to the amount transported into the membrane from the feed. This situation depended mainly on the combined influences of the gel layer and fouling in the membrane. (C) 2010 Society of Chemical Industry